Stem and envelope for electron discharge devices



July 7, 1964 H. v. KNAUF, JR

STEM AND ENVELOPE FOR ELECTRON DISCHARGE DEVICES 2 Sheets-Sheet 1 Filed March '7, 1961 PRIOR ART PRIOR- ART INVENTOR. HARRY VK/vAuF, JR.

July 7, 196.4 H. v. KNAUF, JR 3,140,418

' s'nzu AND ENVELOPE FOR ELECTRON DISCHARGE DEVICES Filed March 7, 1961 2 Sheets-Sheet 2 IN VEN TOR.

HARRY MKA/AUF,

United States Patent 3,140,418 STEM AND ENVELOPE FOR ELECTRON DISCHARGE DEVICES Harry V. Knauf, Jr., Mountainside, NJ assignor to Radio Corporation of America, a corporation of Delaware Filed Mar. 7, 1961, Ser. No. 93,986 9 Claims. (Cl. 313-266) My invention relates to electron discharge devices and more particularly to an improved stem and envelope construction for facilitating manufacture of said devices.

In one form of electron discharge device, the electrode assembly is supported on a stem comprising a header member of ceramic material of fiat disc-like or wafer form and the electrode lead-in and support wires which extend through and are sealed in the header member. The stem and electrode assembly are mounted within a tubular envelope having a base portion of larger transverse dimension than the rest of the envelope. The base portion of the envelope, some times referred to as a shell, is provided with integral oppositely disposed orienting lugs extending from the base portion and of arcuate cross-section of different arcuate dimensions. The periphery of the header member is sealed vacuum tight to the inner wall of the base portion of the envelope.

The envelope is provided with radially inwardly directed projections or shoulders providing positioning and supporting elements for the header member during manufacture. The header member in inverted position is received within the inverted envelope during manufacture. These radially inwardly directed positioning and supporting elements are formed preferably in an intermediate portion of the envelope between the base portion and the remainder of the envelope. This intermediate portion may be an inwardly flared or tapered portion tapering away from the base portion. These inwardly directed projections have supporting surfaces lying in a common plane normal to the longitudinal axis of the tube. With the described construction, the header member is properly supported within the base portion of the envelope during bakeout and exhaust with a minimum of surface contact between the header member and the inner wall of the envelope. This arrangement provides a free exhaust path between the flat inner surface of the header member and the inner wall of the envelope. Further, since there is a loose fit between the peripheral surface of the header member and the inner wall of the base portion of the envelope the gases generated during exhaust may readily escape from the envelope. The header member is provided with a metalized peripheral surface which is brazed to the inside wall of the base portion of the envelope after bakeout and exhaust to seal the envelope vacuum ti ht.

Briefly, the processing of the device is as follows. A ring of brazing material is placed within the base portion with the header member to lie next to the inner wall of the base member. This assembly is then placed within an evacuating exhaust and sealing apparatus. The assembly is then subjected under vacuum to a temperature sufficiently high to out-gas the electrodes and at the same time activate the cathode. The gases escape from the envelope between the header and envelope wall and enter into the exhaust chamber of the exhaust and sealing apparatus. After this heating and exhausting step, the tube is subjected to a higher temperature for causing the brazing ring to melt and braze the peripheral surface of the header member to the inner wall of the base portion of the envelope.

As pointed out above, in order to provide an exhaust path, the fit between the peripheral portion of the base wafer or header member and the inside wall of the en- 3,140,418 Patented July 7, 1964 velope shell must be relatively loose. As a result, difficulty has been experienced in attempting to maintain the proper orientation between the lead pins and the orienting lugs on the shell. In addition to this, a pulling or lifting of the base wafer or header often occurred in an axial direction, due to high gas pressure during exhaust and due to capillary movement of the final seal brazing material. This resulted in improper base wafer-to-shell positioning to such an extent that many finished tubes would not properly enter a tube socket.

Efforts to correct these undesirable conditions have been attempted by employing secondary operations to coin impressions such as dimples in the skirt or base portion of the envelope for the purpose of creating an interference fit with the periphery of the wafer. Additional dimples in the skirt adjacent opposite surfaces of the header and arranged in a triangular pattern were also added to lock the base wafer in position after assembly. These approaches were not entirely satisfactory because the constructions were too rigid and could not be made sufficiently flexible to accommodate the mating parts tolerances, that is, the dimensional tolerances of the wafer and shell. In addition, the lock-in dimples failed to securely hold the parts due to material springback of the envelope. Springback results when the pressure of the dimpling device is removed from the external surface of the shell, the envelope being flexed slightly inwardly on applying dimpling pressure. Furthermore, the dimpling pressure in many instances caused the ceramic wafer to fracture when tolerances of disc or base wafer diameter exceeded maximum limits and when the wafer was tipped in the envelope.

It is therefore an object of my invention to provide an electron discharge device of the type described having an improved stem and envelope construction which while providing an optimum free exhaust path between the envelope and the header member during the bakeout and exhaust steps in the manufacture of such devices and which nevertheless prevents pufiing or lifting of the base wafer or header.

A further and more specific object of my invention is to provide such an improved stem and envelope assembly which eliminates the need for secondary operations at assembly but which nevertheless insures that the mating parts remain in proper relationship after assembly and throughout the bakeout, exhaust and main sealing operations.

An electron discharge device in which the invention may be embodied includes a tubular envelope having at one end a base portion which may be of larger transverse section than the rest of the envelope. The envelope may be provided between the base portion and the remainder of the envelope with an inwardly flared or inwardly tapered portion. The envelope is preferably provided with a plurality of inwardly directed projections or shoulders having supporting surfaces lying in a plane normal to the longitudinal axis of the tube envelope. These projections provide positioning and supporting elements to insure that the base Wafer is properly positioned transversely of the longitudinal axis of the envelope during assembly operations.

In accordance with my invention I provide the base portion of the envelope which is of comparatively thin metal with a plurality of spaced chordal flats. These chordal flats provide a spring type of press fit that will accommodate the normal tolerances of the mating parts while providing the necessary exhaust clearances. When the header is assembled within the base portion, the chordal flats grip the periphery of the disc or wafer at spaced points around the periphery of the wafer with a spring type press fit which is not disturbed during processing of the device.

In the drawings:

FIG. 1 is a longitudinal section showing the construction of a prior art type of electron discharge device;

FIG. 2 is a bottom plan view of FIG. 1;

FIG. 3 is a side elevation of an electron discharge device employing the invention and showing the chordal flats in the envelope;

FIG. 4 is a section taken along the line 44 of the envelope of the device shown in FIG. 1 prior to the reception of the wafer and mount assembly; and

FIG. 5 is a bottom view of the envelope shown in FIGS. 3 and 4 with the stem wafer received within the base portion of the envelope and illustrates the spring fit between the envelope and the base water or header prior to scaling.

In FIG. 1 which illustrates a prior art form of the electron discharge device, the flat disc header member or base Wafer 1% may be a ceramic disc. Extending therethrough and sealed therein are the lead-in conductor and supporting wires 11 and ill for supporting and providing electrical connections to the electrodes mounted on the inner ends thereof. These electrodes may include the cathode 12, the grid 13 and the anode 14 which are supported respectively upon the flange supports 15, 16 and 17. These flanges, in turn, are supported on the inner ends of the lead-in and support conductors H and 11. The envelope includes the elongated portion 20 and the base portion 22 of larger diameter than the elongated portion 29. The base portion receives the header member which is positioned by the inwardly directed projections or shoulders 33. The header member 10 which is provided with a metalized periphery is brazed at 10 vacum tight to the inner wall of the base portion 22 when the brazing ring 23 is heated to brazing temperature.

The base portion of the envelope is provided with oppositely disposed orienting and positioning lugs 26 and 27. These lugs register with arcuate shaped apertures in a socket to insure that the lead-ins are inserted Within the proper apertures in the socket to make the proper connections between the different electrodes and the socket connections.

In baking out, exhausting and sealing the electron discharge device assembly, the envelope, header member and electrode assembly with leads properly oriented with the positioning lugs are passed through an evacuating exhaust and sealing apparatus and in the inverted position shown in FIG. 1.

The entire assembly is first subjected to a temperature sufficiently high to bakeout the electrodes and partially activate the cathode. Since the header. member 10, merely rests upon the radially directed supporting elements 33 and since there is a loose fit between the inner wall'of the envelope and the header member, gases may escape from the inside of the envelope to the interior of the exhaust apparatus.

It is the construction described above and the processing utilized which results in the problems previously described.

An electron discharge device utilizing my invention may include the various elements disclosed in FIGS. 1 and 2 and therefore these are not shown in FIG. 3 or further described. Like numerals indicate like parts in all of the figures.

In accordance With my invention I provide the metal shell skirt or base portion 22 of the envelope with preferably six chordal flats 30 which are formed with the bottom portion 30' of each flat spaced from the end of the envelope. While a smaller number of flats, for example, three, can be used, I prefer six flats to obtain the desired space between the metal shell skirt and the base wafer or header member 10 to allow proper exhaust of gases from within the envelope and also to provide a path wherein a good capillary flow of brazing material will occur when the proper brazing temperatures are reached. The six flats provide a sufficiently tight fit with the periphery of the Wafer to avoid radial rotation of the wafer 10 with respect to the envelope and also prevent longitudinal movement of wafer 16 with respect to the envelope. The flats are formed to be tangent to a circle the diameter of which is slightly smaller than the diameter of the header disc or wafer, that is, the periph eral surface of the wafer lies in the surface of a cylinder of larger diameter than said circle.

In assembly, the base wafer 10 is inserted Within the tubular portion of the envelope far enough to contact the ends 30 of the flats. At this point a suitable fixture may be used to press the base wafer into engagement with the six flats to a predetermined position, with the base wafer square with respect to the metal shell, that is, transverse to the longitudinal axis of the envelope. Preferably, the radially directed positioning elements are relied upon to insure that the wafer lfl is in proper position Within the envelope. As an alternative, it is possible to have the shell of the same diameter throughout and rely upon the flats 30 alone to hold the wafer in its proper position by providing stop means on the fixture so that insertion is limited to a predetermined distance within the envelope shell.

The advantages of an envelope shell 2%) made according to my invention is that the spring action of the flats provides a spring action which is equally effective over the entire range of thermal and base wafer tolerances. The six points of relative area contact at 311 (FIG. 5) provide improved thermal conditions by conduction for uniform brazing and better main seals. condition of the metal shell with respect to ceramic base wafer provides a gentle spring-out of the shell skirt as shown at areas 31 bowing the chordal flats 3t outwardly. The area contact and springout prevent chipping or fracture of the ceramic base Wafer 10 during assembly. The metal shell does not relax its fit, even at brazing temperatures, thus preventing base wafer tilt due to lifting or pufling during the exhaust operations. The six chordal flats provide better centering of the base wafer in the shell skirt resulting in a more uniform spacing around the periphery between each flat for exhaust clearance. This centering also aids in making the final brazed seal due to the uniform capillary condition which is thereby provided because of the even spacing between the periphery of the base Wafer and the Wall of the enve lope. The envelope shells can be made initially by conventional methods so that secondary operations at assembly to secure the parts in proper relationship during assembly, exhaust, and sealing operations are eliminated. Lastly, with the construction described, devices can be processed whether the devices are inverted or right side up..

What is claimed is:

1. An electron discharge device including an envelope having a metal base portion, the wall of the base portion having a plurality of chordal flats providing spring-like engaging elements, an insulating disc received within said base portion, said flats engaging the periphery of said disc with a compressive fit, said disc supporting an electrode assembly within said envelope and sealed vacuum tight at its periphery to the inner Wall of the base portion of said envelope.

2. An electron discharge device including an envelope having a metal base portion, the wall of the base portion being initially provided with a plurality of chordal flats lying tangent to a' circle and providing spring-like engaging elements, an insulating disc received within said base portion and having a periphery lying in the surface of a cylinder having a diameter greater than the diameter of said circle, said flats engaging the periphery of said disc with a compressive fit and being slightly sprung out, said disc supporting an electrode within said envelope and sealed vacuum tight at its periphery to the inner Wall of the base portion of saidenvelope.

The press fit 3. An electron discharge device including an envelope having a metal base portion, the wall of the base portion having a plurality of spaced chordal flats providing springlike engaging elements, an insulating disc received within said base portion, said flats engaging the periphery of said disc with a compressive fit, electrode means supported on said disc within said envelope, lead-in conductor means extending through and sealed to said disc and connected to said electrode means, said disc being sealed vacuum tight at its periphery to the inner wall of the base portion of said envelope, said base portion being provided with oppositely disposed lugs of arcuate shape extending from said base portion and oriented with respect to said lead-in conductor means.

4. An electron discharge device including an envelope having a base portion at one end, said envelope having a plurality of positioning elements extending radially inwardly of the envelope adjacent the base end of the envelope, the wall of the base portion of the envelope being provided with a plurality of spaced chordal flats, an insulating disc received within said base portion of the envelope, said flats engaging the periphery of said disc with a compressive fit, said disc being positioned within said envelope by said positioning elements, said disc supporting an electrode within said envelope and sealed vacuum tight at its periphery to the inner wall of the base portion of said envelope.

5. An electron discharge device including an envelope having a metal base portion at one end, the wall of the base portion of the envelope being initially provided with a plurality of spaced flats, tangent to a circle, an insulating disc received within said portion of the envelope, said disc having a diameter greater than said circle, said flats engaging the periphery of said disc with a compressive fit and being slightly sprung out, said disc being positioned within said base portion and spaced from the end of said envelope, said disc supporting an electrode within said envelope and sealed vacuum tight at its periphery to the inner wall of the base portion of said envelope.

6. An electron discharge device including an envelope having a metallic base portion at one end, said base portion having oppositely disposed locating lugs integral therewith and extending therefrom, said envelope having a plurality of positioning elements extending radially inwardly of the envelope adjacent the base end of the envelope, the wall of the base portion of the envelope being provided with a plurality of spaced chordal flats, an insulating disc received within said base portion of the envelope, said flats engaging the periphery of said disc with a compressive fit, said disc being positioned within said envelope by said positioning elements, said disc supporting an electrode within said envelope, a lead-in conductor extending through and sealed in said disc and connected to said electrode, said disc being sealed vacuum tight at its periphery to the inner wall of the base portion of said envelope, said lead-in conductor and said locating lugs being oriented with respect to each other.

7. An electron discharge device including a stem comprising a flat header member having a peripheral surface normal to the flat surfaces of said header member, an electrode supported on one of said flat surfaces, an envelope within which said stem and electrode are received, said envelope having at one end a metal base portion within which said header member is received for closing said envelope, the intermediate portion of said envelope between the tubular portion and the base portion being formed to provide a space between said intermediate portion and the inner flat surface of said header member, said space providing a free exhaust path between said intermediate portion and said header member during bakeout and exhaust, said envelope being provided with a plurality of inwardly projected positioning means for positioning said header member, the wall of said base portion being provided with a plurality of chordal flats having spring-like characteristics, said flats engage the periphery of said header member with a compressive fit whereby said flats exert a compressive spring action on said periphery at the areas of contact between said header member and said flats, said header member being sealed vacuum tight at its periphery to the inner wall of the base portion of said envelope.

8. An electron discharge device including a stem comprising a flat header member having a peripheral surface normal to the flat surfaces of said header member, electrode means supported on one of said flat surfaces, an envelope within which said stem and electrode means are received, said envelope having at one end a metal base portion within which said header member is received for closing said envelope, the intermediate portion of said envelope between the tubular portion and the base portion being formed to provide a space between said intermediate portion and the flat surfaces of said header member, said space providing a free exhaust path between said intermediate portion and said header member during bakeout and exhaust, the wall of said base portion being provided initially with a plurality of chordal flats having spring-like characteristics, said flats engaging the periphery of said header member with a compressive fit contact whereby said flats exert a spring-like compressive action on said periphery at the areas of contact between said header member and said flats, said header member being sealed vacuum tight at its periphery to the inner wall of said base portion.

9. An electron discharge device including a stem comprising a flat header member having a peripheral surface normal to the flat surfaces of said header member, electrode means supported on one of said flat surfaces, an envelope within which said stem and electrode means are received, said envelope having at one end a metal base portion within which said header member is received for closing the envelope, the intermediate portion of said envelope between the tubular portion and base portion being formed to provide a space between the wall of said envelope and said header member, said space providing a free exhaust path between the inner wall of the envelope and said header member during bakeout and exhaust, said base portion having a plurality of positioning lugs extending therefrom, the wall of said base portion being provided with a plurality of chordal flats having spring-like characteristics, said flats engaging the periphery of said header member with a compressive fit whereby said flats exert a compressive spring action on said periphery at the areas of contact between said header member and said flats, conductor lead-in means extending through said header and sealed therein and connected to said electrode means, said header member being sealed vacuum tight at its periphery to the inner wall of the base portion of said envelope, said lugs and said conductor means being oriented with respect to each other.

References Cited in the file of this patent FOREIGN PATENTS 914,686 France o r. 15, 1946 

1. AN ELECTRON DISCHARGE DEVICE INCLUDING AN ENVELOPE HAVING A METAL BASE PORTION, THE WALL OF THE BASE PORTION HAVING A PLURALITY OF CHORDAL FLATS PROVIDING SPRING-LIKE ENGAGING ELEMENTS, AN INSULATING DISC RECEIVED WITHIN SAID BASE PORTION, SAID FLATS ENGAGING THE PERIPHERY OF SAID DISC WITH A COMPRESSIVE FIT, SAID DISC SUPPORTING AN ELECTRODE ASSEMBLY WITHIN SAID ENVELOPE AND SEALED VACUUM TIGHT AT ITS PERIPHERY TO THE INNER WALL OF THE BASE PORTION OF SAID ENVELOPE. 